Novel Co-Ti-V-base superalloys reinforced by L12-ordered γ' phase

The influences of alloying elements Al and Ni to a Co-Ti-V master alloy on microstructures, phase stabilities and high-temperature mechanical properties have been investigated. A two-phase microstructure gamma/gamma' with ultrahigh gamma' volume fraction was designed in the Co-Ti-V (master alloy), Co-Ti-V-Al (Al-modified) and Co-Ti-V-Ni (Ni-modified) alloys. Al shows a slight tendency to partition into gamma', while Ni exhibits almost equal distribution between the gamma and gamma' phases. Al is found to increase the volume fraction and solvus temperature of gamma'. The solvus temperatures of gamma' in the master alloy, Al-modified and Ni-modified alloys exceed that of Co-9Al-9W alloy (1000 degrees C) by 91, 112 and 82 degrees C, respectively. The flow stresses of the designed alloys exhibit an anomalous positive dependence on temperature rising from 600 to 750 degrees C. The strengths of the master alloy and Ni-modified alloys are not only higher than that of traditional Co-base superalloy MAR-M 302 at the temperature ranging from 700 to 1000 degrees C, but also comparable with that of the commercial Ni-base superalloy IN-939 between 850 and 1000 degrees C. In conclusion, the present Co-Ti-V-base alloys reinforced by gamma' are suggested as potential candidates for high-temperature utilizations.